Supported noble metal catalysts are used in a large number of commercially important applications including hydrogenation, dehydrogenation, isomerization, naphtha reforming, hydrocracking, oxidation, automotive exhaust catalysts, and fuel cells. The catalytic activity of metallic sites of these catalysts depends upon (i) number of metal sites (ii) size of metal site (iii) metal support interaction (iv) noble metal cluster orientation (plane). The orientation of noble metal plane is critical for the structure sensitive reactions which involve breaking or making of C—C, N—N or C—O bonds at the metal site.
Hydrogenation/dehydrogenation reactions are of prime importance to refining industry. These reactions are also inevitable part of the hydroisomerization process used for production of high octane gasoline; dewaxed diesel oil and high quality lube oil with excellent cold low properties. Moreover the metal site activity for these catalytic reactions is scarcely influenced by the orientation of noble planes but is strongly dependent on the dispersion and loading of metal sites.
U.S. Pat. No. 4,209,384 describes a method of preparation of a catalyst consisting of platinum metal loaded on to a mordenite-alumina support for hydroprocessing reaction. The catalyst is prepared by incorporating the platinum component with a solution having a pH greater than 6.
U.S. Pat. No. 4,568,656 describes a process for loading platinum on zeolite-L using an aqueous solution containing a platinum salt and a non-platinum metal salt. The non-platinum metal salt is added in certain critical amount to avoid blockage of pores and to ensure that no acid sites are formed during the platinum loading process.
U.S. Pat. No. 7,141,529 discloses a process for isomerization of straight chain or slightly branched paraffins having ten or more carbon atoms using an intermediate pore size molecular sieve modified with metals and additionally loaded with Group VII metal or metals.
EP 0145289 discloses a process for reforming naphtha which employs a reforming catalyst comprising a zeolite containing at least one Group VIII noble metal. The noble metal is highly dispersed throughout the zeolite and the optionally used binder. The reforming catalyst is capable of terminally cracking various organic compounds and exhibits sustained activity maintenance under reforming conditions and improved selectivity for aromatization products.
U.S. Pat. No. 4,814,306 discloses a method for controlled noble metal exchange over zeolite using bulky organic bases by controlling pH during metal loading step.
Highly dispersed platinum particles on HZSM-5 zeolite have been prepared and the effect of pre-treatment process of Pt(NH3)4]2+ on the dispersion of platinum particles has been studied (Van Santeen et al., Journal of Catalysis, 1997, 167, 417).